Geomorphology is the systematic description, analysis, and understanding of landscapes and the processes that change them. Over time, the land surface is shaped by uplift from within the earth, and the effects of water, wind, and ice. Hydrology is the science dealing with the properties, distribution, and circulation of water. A stream's physical appearance and character are the result of its adjustment to the quantity of water and extent of erosion within its watershed.
A reach is a continuous section of a stream or river. The stage of a flow is the elevation of the water surface. Stream channels contain alternating regions of riffles and pools. During low flows, riffles are regions of shallow, rapid flow. At the time of high flows, the riffles are "drowned out". The velocity of water in pools is lower than in the riffles. Meanders are freely-swinging, winding stream channels.
Meandering stream
Topography describes the shape of a portion of the earth's surface including its elevations and the position of physical and cultural features.At bankfull stage, water flow fills a stream channel to the top of its banks just to the point where water begins to overflow onto the adjacent floodplain. Infrequent extreme floods may cause significant changes in stream channels. However, bankfull stage flows transport the greatest quantity of soil and stone over time, because the bankfull stage occurs about once every year or two. The bankfull stage is related to channel dimensions such as width, and to the meandering pattern of a stream. Entrenchment describes the relationship of the river or stream to its landscape. Entrenchment is the degree to which a stream or river is cut into the valley floor, and is calculated as the width of the flood-prone area to the stream's width at bankfull stage.
Field determination of the flood-prone area is utilized in determining the degree of entrenchment to avoid having to map an arbitrary or political flow level such as the "100 year floodplain". Rosgen, 1996, pp. 5-15,19.
The width-to-depth ratio is defined as the ratio of the bankfull surface width to the average depth of the bankfull channel. The width-to-depth ratio is important in understanding a stream's adjustments to the water's energy in its channel, and the ability of various discharges within the channel to move sediment.
Sinuosity is the ratio of stream length to valley length. A straight stream has a sinuosity of 1. Stream meander characteristics are directly related to sinuosity. A closer approximation to equilibrium is achieved by meandering than non-meandering stream pattern. Leopold, 1992, p.303.
Channel bed and bank materials influence the stream's cross-section shape and linear pattern. These materials also determine the extent of sediment transport. An assessment of the nature and distribution of channel materials is important for interpreting the biological function and stability of rivers. Rosgen, 1996, p. 5-25.
The slope of the water surface is a major determinant of river and stream form, structure, and performance. Slope is determined by measuring the rise of the stream water surface over a distance greater than 20 times the stream's width.
